[kvm-devel] [PATCH] Handle vma regions with no backing page

[Anthony Liguori]

This patch allows VMA's that contain no backing page to be used for guest
memory.  This is a drop-in replacement for Ben-Ami's first page in his direct
mmio series.  Here, we continue to allow mmio pages to be represented in the
rmap.

Signed-off-by: Anthony Liguori <[EMAIL PROTECTED]>

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index f095b73..11b26f5 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -531,6 +531,7 @@ pfn_t gfn_to_pfn(struct kvm *kvm, gfn_t gfn)
        struct page *page[1];
        unsigned long addr;
        int npages;
+       pfn_t pfn;
 
        might_sleep();
 
@@ -543,19 +544,36 @@ pfn_t gfn_to_pfn(struct kvm *kvm, gfn_t gfn)
        npages = get_user_pages(current, current->mm, addr, 1, 1, 1, page,
                                NULL);
 
-       if (npages != 1) {
-               get_page(bad_page);
-               return page_to_pfn(bad_page);
-       }
+       if (unlikely(npages != 1)) {
+               struct vm_area_struct *vma;
+
+               vma = find_vma(current->mm, addr);
+               if (vma == NULL) {
+                       get_page(bad_page);
+                       return page_to_pfn(bad_page);
+               }
+
+               BUG_ON(!(vma->vm_flags & VM_IO));
 
-       return page_to_pfn(page[0]);
+               pfn = ((addr - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
+               BUG_ON(pfn_valid(pfn));
+       } else
+               pfn = page_to_pfn(page[0]);
+
+       return pfn;
 }
 
 EXPORT_SYMBOL_GPL(gfn_to_pfn);
 
 struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn)
 {
-       return pfn_to_page(gfn_to_pfn(kvm, gfn));
+       pfn_t pfn;
+
+       pfn = gfn_to_pfn(kvm, gfn);
+       if (pfn_valid(pfn))
+               return pfn_to_page(pfn);
+
+       return NULL;
 }
 
 EXPORT_SYMBOL_GPL(gfn_to_page);
@@ -568,7 +586,8 @@ EXPORT_SYMBOL_GPL(kvm_release_page_clean);
 
 void kvm_release_pfn_clean(pfn_t pfn)
 {
-       put_page(pfn_to_page(pfn));
+       if (pfn_valid(pfn))
+               put_page(pfn_to_page(pfn));
 }
 EXPORT_SYMBOL_GPL(kvm_release_pfn_clean);
 
@@ -593,21 +612,25 @@ EXPORT_SYMBOL_GPL(kvm_set_page_dirty);
 
 void kvm_set_pfn_dirty(pfn_t pfn)
 {
-       struct page *page = pfn_to_page(pfn);
-       if (!PageReserved(page))
-               SetPageDirty(page);
+       if (pfn_valid(pfn)) {
+               struct page *page = pfn_to_page(pfn);
+               if (!PageReserved(page))
+                       SetPageDirty(page);
+       }
 }
 EXPORT_SYMBOL_GPL(kvm_set_pfn_dirty);
 
 void kvm_set_pfn_accessed(pfn_t pfn)
 {
-       mark_page_accessed(pfn_to_page(pfn));
+       if (pfn_valid(pfn))
+               mark_page_accessed(pfn_to_page(pfn));
 }
 EXPORT_SYMBOL_GPL(kvm_set_pfn_accessed);
 
 void kvm_get_pfn(pfn_t pfn)
 {
-       get_page(pfn_to_page(pfn));
+       if (pfn_valid(pfn))
+               get_page(pfn_to_page(pfn));
 }
 EXPORT_SYMBOL_GPL(kvm_get_pfn);
 

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